This invention relates generally to hydrocyclone apparatus and methods for controlling the density of discharging underflow.
Hydrocyclones are commonly used in many industries for carrying out concentrating, clarifying and classifying operations on various mineral slurries, pulps and liquids containing undissolved solids. Briefly, when disposed in upright position, a hydrocyclone consists of a separating chamber that is annular in section with a lower conical portion having an underflow discharge opening at its apex end. The separating chamber also has means forming an inlet opening connected tangentially with the upper head portion of the chamber, and means forming an overflow outlet which communicates with a vortex finder disposed axially within the head portion of the chamber. When in operation, feed is supplied under pressure to the inlet and swirling movement of the body of material within the chamber causes centrifugal separation whereby heavier separated solids are discharged in an underflow from the apex end of the chamber, and the lighter solids are discharged through the vortex finder and the overflow outlet. For concentrating, or where it is desired to provide a clarified overflow, the operation is such that substantially all of the solid material of the feed is discharged with the underflow. For classification, heavier solids are discharged in the underflow and lighter solids in the overflow.
A common problem in the operation of hydrocyclones has been the maintenance of a constant high density (solid to liquid ratio) underflow material while operating under conditions where the density of cyclone feed fluctuates over wide limits. Such fluctuations are experienced for example in mineral slurries produced by continuously operating product preparation circuits. By way of example, in instances where a sand-gravel preparation circuit is supplying feed to a hydrocyclone, the density of the feed may vary from less than 1% to more than 25%, with the result that the underflow is subjected to corresponding fluctuations in density. Such variations may cause serious resulting problems in the handling and further processing of the underflow.
In the past, various methods and types of equipment have been employed in an effort to control the density of the underflow. For example, in some instances variations in density of the overflow have been detected by various devices, with the detecting device connected to control the circuit which is preparing the feed. Such equipment is relatively expensive and the control provided is not as accurate as is frequently desired, due to deficiencies in the detecting devices, inability to effectively control the preparation circuit, or both. Less elaborate devices that have been employed include collapsible tubing of resilient material, flap valves, and counterbalanced piping arrangements applied to the apex of the hydrocyclone to effect some control over the discharge of underflow in accordance with change in density. Use of such devices has resulted in increased maintenance requirements of the hydrocyclone circuit, cyclone choking or plugging, and aberrant performance. In addition, such devices do not provide maintenance of the underflow density within the flow limits frequently desired.